It is known that semiconductors with a broad band gap, such as GaN or ZnO, are suitable for utilization in detectors of ionising radiation. The materials of this type show a short decay time of excited luminescence in the order of 1 ns and are radiation resistant. The advantage of GaN is the possibility of its preparation in higher crystallographic quality and in the form of homogenous epitaxial layers, applied onto large surfaces of monocrystalline substrates in up to several different layers on top of each other which results in the creation of heterostructures. These heterostructures show low non-radiant losses and a narrow luminescence maximum.
The patent document U.S. Pat. No. 7,053,375 B2 describes a semiconductor scintillator, including group III elements from the periodic table in compound with nitrogen in the form of a semiconductor for the excitation with ionising radiation. This semiconductor compound is structured into a layer, formed on a generally described substrate. Furthermore, there might be between the semiconductor layer and the substrate a semi-layer to smoothen/improve the semiconductor structure that is called a buffer layer. Various nitride compounds with a group III element and their alloys may be utilized in different layers applied over each other and create heterostructures.
Another known patent document U.S. Pat. No. 8,164,069 B2 describes a fluorescent agent reaction to the electron incidence with light emission, luminescence. The fluorescent agent includes a carrier monocrystalline substrate, nitride semiconductor sandwich structure, in which barrier layers alternate with layers representing potential wells. The semiconductor layers create a heterostructure which is formed on the surface of one substrate side. The potential wells are preferentially created with an InxGa1-xN alloy semiconductor.
A disadvantage of above mentioned solutions is that they do not consider the strong piezoelectric field, which is formed between interfaces of layers with different composition. This piezoelectric field decreases the electron-hole wave function overlap and consequently considerably decreases the luminescence intensity and prolongs the luminescence decay time. This means that the scintillator will have less intensive and slower response. The next disadvantage of the above stated solutions consist of the fact that during the incidence of the ionising radiation a relatively large amount of energy is consumed for a non-radiative electron-hole recombination in the semiconductor material. The presence of potential wells improves this rate, however, the resulting ratio of the consumed energy for the radiative and non-radiative recombination still does not suffice. The attainment of a higher number of potential wells in the semiconductor layer that would improve the resulting ratio of recombination energies is prevented by the increased strain in the structure due to the increasing number of the InxGa1-xN wells, caused by the different lattice constant of InxGa1-xN.
The task of the invention is to create a monocrystalline nitride scintillation detector for the detection of ionising radiation that would eliminate the drawbacks of the known solutions, suppress the influence of piezoelectric field and decreased the strain in the structure, which would increase the intensity and speed of luminescent response to the incident ionising radiation.